The invention concerns a heat-sterilizable spiral-wound, cross-flow, membrane filter cartridge.
Sterilizable filter modules are required for filter processes in the fields of pharmaceuticals, biotechnology, laboratory research, as well as in the food and beverage industries. Such applications require the separation of microorganisms from the fluid to be filtered, while at the same time avoiding contamination of the fluid. Filter equipment and filter modules may be sterilized by the action of chemicals or by heat. The use of chemicals has a series of disadvantages due to chemical attack, such as requirements for additional rinsing operations, an environmentally friendly disposal of the residues, and damage to the membranes and to other elements of the module. By the use of heat sterilization, one is spared the controlled rinsing of disinfecting chemicals and the difficulties surrounding the disposal of residues. Typically, heat sterilization is carried out either by heating the equipment with hot water to at least 80.degree. C. for at least 30 minutes, or with superheated steam at a temperature between 120.degree. and 140.degree. C., the latter being conducted either in autoclaves or by in-line injection of steam.
Although hot water sterilization destroys most bacteria, yeasts, and molds, complete sterilization is not always attained. Sterilization in an autoclave is subject to the danger of recontamination upon removal and reconnection of the module to the sterilized filtration plant equipment. Because of these drawbacks, the preferred sterilization method is the in-line, superheated steam procedure.
Because of their construction and the materials employed, current commercially available spiral-wound cross-flow modules cannot withstand the thermal and pressure demands of heat sterilization. The temperatures used in superheated steam sterilization and in autoclaves run up to 140.degree. C. and pressures run as high as 4.times.10.sup.5 Pa. Such extreme conditions on the one hand cause shrinkage of up to 10% in the case of many of the polymers for spiral-wound modules, and on the other hand cause a kind of radial expansion of the wound module which leads to an irreversible loosening of the spiral-wound coil, which results in a telescopic protrusion of the module. The radial expansion and telescoping protrusion in turn lead to bypassing and blockages in the module and to damage of the module construction and the membranes, rendering the filter modules useless.
It is therefore a principal object of the present invention to provide a spiral-wound cross-flow filter module having organic polymer membranes which are heat-sterilizable and mechanically stable under extreme sterilizing conditions.
This object and others will become apparent upon consideration of the invention, which is summarized and described in detail below.